I can't change my brightness in JK2. The brightness bar line will move, but there will be no effect in game or in the menu. At present, the brightness the game is stuck at is too dark to play.
Thats a common problem with Win XP. You can find help here:
http://www.lucasforums.com/showthread.php?s=&threadid=51444)
In addition, no settings are retained when I leave the game. Customized controls and display options (including brightness) are back to default when I restart.
Thats probably because you use the safemode shortcuts in your startmenu.